Copending Application U.S. Ser. No. 09/864,386, filed May 24, 2001. entitled xe2x80x9cPhotochromic Gyricon Display,xe2x80x9d with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, Peter M. Kazmaier, Erwin Buncel, and James Wojtyk, the disclosure of which is totally incorporated herein by reference, discloses a display comprising an arrangement of a plurality of optically anisotropic rotatable elements, each of said rotatable elements having a surface in contact with an enabling fluid, said rotatable elements being electrically dipolar in the presence of the enabling fluid and thus being subject to rotation upon application of an electric field, said rotatable elements being free to rotate in place but not free to translate substantially so as to disrupt the arrangement of rotatable elements, wherein a first portion of said surface contains a mixture of a chelating agent and a spiropyran material of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, and wherein a second portion of said surface contains substantially no spiropyran.
Copending Application U.S. Ser. No. 09/864,902, filed May 24, 2001, entitled xe2x80x9cPhotochromic Electrophoretic Ink Display,xe2x80x9d with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, Peter M. Kazmaier, Erwin Buncel, and James Wojtyk, the disclosure of which is totally incorporated herein by reference, discloses an electrophoretic ink comprising a suspending fluid and, suspended in the suspending fluid, a plurality of particles comprising a mixture of a chelating agent and a spiropyran material of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, said particles being free to migrate within said suspending fluid under the influence of an electric field.
Copending Application U.S. Ser. No. 09/864,475, filed May 24, 2001, entitled xe2x80x9cMarking Particles,xe2x80x9d with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, Peter M. Kazmaier, Erwin Buncel, and James Wojtyk, the disclosure of which is totally incorporated herein by reference, discloses marking particles comprising a first polymer, a second polymer, a chelating agent, and a spiropyran material of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2. The marking particles comprise a core containing the first polymer in which is dispersed the chelating agent and the spiropyran and encapsulated within a shell of the second polymer formulated by an interfacial polymerization.
Copending Application U.S. Ser. No. 09/864,535, filed May 24, 2001, entitled xe2x80x9cMarking Particles,xe2x80x9d with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, and Peter M. Kazmaier, the disclosure of which is totally incorporated herein by reference, discloses marking particles comprising a resin, a chelating agent, and a spiropyran material which is of the formula 
The marking particles are prepared by an emulsion aggregation process.
The present invention is directed to processes for the preparation of photochromic high density storage media and imaging processes therewith. More specifically, the present invention is directed to compositions and processes for the preparation of optically addressable, high density, three-dimensional photochromic storage media for use in, for example, digital recording media and processes. One embodiment of the present invention is directed to a matrix composition which: comprises (a) a discrete phase comprising an ordered array of core particles containing a first resin, and (b) an annealed continuous phase comprising a second resin, wherein at least one of the first resin and the second resin contains a chelating agent and a spiropyran compound of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, wherein if the spiropyran compound is irradiated then the optical properties of the resin containing the spiropyran compound change. Another embodiment of the present invention is directed to a composition comprising a matrix which comprises particles comprising a core resin and a shell resin thereover, wherein at least one of the core resin and the shell resin contains a chelating agent and a spiropyran compound of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, wherein the shell resin is the continuous phase of the matrix, wherein the spiropyran compound can produce changes in the optical and photoactive properties of the resin containing the spiropyran when irradiated. Yet another embodiment of the present invention is directed to a process which comprises (a) organizing into an array particles comprising a core resin and a shell resin, wherein at least one of the core resin and the shell resin contains a chelating agent and a spiropyran compound of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2; and (b) heating the array to cause the shell resin to melt, partially flow, then harden on cooling, to fix the particles into a storage medium comprising the particles as a discrete phase and the shell resin as a continuous phase. Still another embodiment of the present invention is directed to a process which comprises fusing an array of particles comprising a core resin with a shell resin thereover to fix the particles into a matrix, wherein at least one of the core resin and the shell resin contains a chelating agent and a spiropyran compound of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, and wherein the core resin comprises a discrete phase and the shell resin comprises a continuous phase of the matrix.
Photochromism in general is a reversible change of a single chemical species between two states having distinguishably different absorption spectra, wherein the change is induced in at least one direction by the action of electromagnetic radiation. The inducing radiation, as well as the changes in the absorption spectra, are usually in the ultraviolet, visible, or infrared regions. In some instances, the change in one direction is thermally induced. The single chemical species can be a molecule or an ion, and the reversible change in states may be a conversion between two molecules or ions, or the dissociation of a single molecule or ion into two or more species, with the reverse change being a recombination of the two or more species thus formed into the original molecule or ion. Photochromic phenomena are observed in both organic compounds, such as anils, disulfoxides, hydrazones, oxazones, semicarbazones, stilbene derivatives, o-nitrobenzyl derivatives, spiro compounds, and the like, and in inorganic compounds, such as metal oxides, alkaline earth metal sulfides, titanates, mercury compounds, copper compounds, minerals, transition metal compounds such as carbonyls, and the like. Photochromic materials are known in applications such as photochromic glasses, which are useful as, for example, ophthalmic lenses.
U.S. Pat. No. 5,952,131 (Kumacheva et al.) and U.S. Pat. No. 6,214,500 (Kumacheva et al.), the disclosures of each of which are totally incorporated herein by reference, disclose a composition including a matrix which comprises particles comprising a core resin and a shell resin thereover, wherein the core resin contains a covalently bonded photosensitive compound, and wherein the shell resin is the continuous phase of the matrix.
U.S. Pat. No. 5,633,109 (Jennings et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous liquid vehicle, a photochromic material, and a vesicle-forming lipid, wherein vesicles of the lipid are present in the ink.
U.S. Pat. No. 5,551,973 (Oliver et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous phase, an oil phase, a, photochromic material, and a surfactant, said ink exhibiting a liquid crystalline gel phase at a first temperature and a liquid microemulsion phase at a second temperature higher than the first temperature.
U.S. Pat. No. 5,593,486 (Oliver et al.), the disclosure of which is totally incorporated herein by reference, discloses a hot melt ink composition comprising (a) an ink vehicle, said ink vehicle being a solid at about 25xc2x0 C. and having a viscosity of from about 1 to about 20 centipoise at a temperature suitable for hot melt ink jet printing, said temperature being greater than about 45xc2x0 C., (b) a photochromic material, (c) an optional colorant, and (d) an optional propellant.
U.S. Pat. No. 5,710,420 (Martin et al.), the disclosure of which is totally incorporated herein by reference, discloses a method of embedding and recovering machine readable information on a substrate which comprises (a) writing data in a predetermined machine readable code format on the substrate with a photochromic marking material having a first state corresponding to a first absorption spectrum and a second state corresponding to a second absorption spectrum; and (b) thereafter effecting a photochromic change in at least some of the photochromic marking material from the first state to the second state.
U.S. Pat. No. 5,759,729 (Martin et al.), the disclosure of which is totally incorporated herein by reference, discloses a toner composition for the development of electrostatic latent images which comprises particles comprising a mixture of a resin and a photochromic material. Another embodiment of the invention is directed to a liquid developer composition for the development of electrostatic latent images which comprises a nonaqueous liquid vehicle and a photochromic material, wherein the liquid developer has a resistivity of from about 108 to about 1011 ohm-cm and a viscosity of from about 25 to about 500 centipoise. Yet another embodiment of the invention is directed to a liquid developer composition for the development of electrostatic latent images which comprises a nonaqueous liquid vehicle, a charge control agent, and toner particles comprising a mixture of a resin and a photochromic material.
James T. C. Wojtyk, Peter M. Kazmaier, and Erwin Buncel, xe2x80x9cEffects of Metal Ion Complexation on the Spiropyran-Merocyanine Interconversion: Development of a Thermally Stable Photo-Switch,xe2x80x9d Chem. Commun. 1998, p. 1703, the disclosure of which is totally incorporated herein by reference, discloses spectrophotometric absorption and fluorescence measurements of spiropyrans 
modified with chelating functionalities, in the presence of Ca2+ and Zn2+, that provide evidence of a thermally stable spiropyran-merocyanine photoswitch that is modulated by the metal cations.
While known compositions and processes are suitable for their intended purposes, a need remains for structures comprising nanoparticles, such as polymer encapsulated resin particles, that are ordered on a macroscopic scale, including thin film and two dimensional media and three-dimensional periodic arrays wherein the storage density is greatly enhanced. In addition, a need remains for media with improved efficiency, improved flexibility, and improved operational economies. Further, a need remains for imaging processes wherein a photosensitive compound is selectively and effectively addressed, thereby forming a stable three-dimensional image therein. Additionally, a need remains for storage media containing photochromic materials. There is also a need for photochromic storage media wherein both resonance forms of the photochromic material are stable. There is also a need for photochromic storage media wherein the two resonance forms of the photochromic material are addressable at different wavelengths. In addition, there is a need for photochromic storage media wherein both resonance forms of the photochromic material are stable for reasonable periods of time without the need for constant irradiation to maintain the resonance form. Further, there is a need for thermally stable photochromic storage media. Additionally, there is a need for photochromic storage media wherein the photochromic shift can be induced rapidly. A need also remains for photochromic storage media wherein the photochromic shift can be both induced rapidly and reversed rapidly.
The present invention is directed to a matrix composition which comprises (a) a discrete phase comprising an ordered array of core particles containing a first resin, and (b) an annealed continuous phase comprising a second resin, wherein at least one of the first resin and the second resin contains a chelating agent and a spiropyran compound of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, wherein if the spiropyran compound is irradiated then the optical, properties of the resin containing the spiropyran compound change. Another embodiment of the present invention is directed to a composition comprising a matrix which comprises particles comprising a core resin and a shell resin thereover, wherein at least one of the core resin and the shell resin contains a chelating agent and a spiropyran compound of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, wherein the shell resin is the continuous phase of the matrix, wherein the spiropyran compound can produce changes in the optical and photoactive properties of the resin containing the spiropyran when irradiated. Yet another embodiment of the present invention is directed to a process which comprises (a) organizing into an array particles comprising a core resin and a shell resin, wherein at least one of the core resin and the shell resin contains a chelating agent and a spiropyran compound of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2; and (b) heating the array to cause the shell resin to melt, partially flow, then harden on cooling, to fix the particles into a storage medium comprising the particles as a discrete phase and the shell resin as a continuous phase. Still another embodiment of the present invention is directed to a process which comprises fusing an array of particles comprising a core resin with a shell resin thereover to fix the particles into a matrix, wherein at least one of the core resin and the shell resin contains a chelating agent and a spiropyran compound of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, and wherein the core resin comprises a discrete phase and the shell resin comprises a continuous phase of the matrix.